1. Field
This disclosure relates generally to reference signals and, more specifically, to techniques for signaling reference signal parameters in a wireless communication system.
2. Related Art
In general, orthogonal frequency division multiplexing (OFDM) systems support high data rate wireless transmission using orthogonal channels. Typically, OFDM systems split data into N streams, which are independently modulated on parallel spaced subcarrier frequencies or tones. The frequency separation between subcarriers is 1/T, where T is the OFDM symbol time duration. Each symbol may include a guard interval (or cyclic prefix) to maintain the orthogonality of the symbols. Usually, OFDM systems have utilized an inverse discrete Fourier transform (IDFT) to generate a sampled (or discrete) composite time-domain signal.
At least some wireless communication systems have used an estimated received signal strength and an estimated carrier to interference and noise ratio (CINR) of a received signal to determine operational characteristics of the systems. As one example, IEEE 802.16e compliant mobile stations are required to estimate a received signal strength indicator (RSSI) and a CINR of a received signal. In general, CINR at a mobile station (MS) may be calculated as the ratio of an RSSI of a serving base station (BS) to summed RSSIs of non-serving BSs added to a white noise power of a receiver of the MS. The RSSI associated with a serving BS may be used by an MS for uplink power control and the CINR, which is reported to a serving BS, may be used by the serving BS to adapt a downlink (DL) transmission rate to link conditions.
Accurate reported CINRs are usually desirable, as inaccurate reported CINRs may impact performance of a wireless network. For example, reporting a CINR that is above an actual CINR may decrease network throughput due to frame re-transmission, while reporting a CINR that is below the actual CINR may cause the serving BS to schedule data rates below a supportable data rate. According to IEEE 802.16e, RSSI and CINR estimates at an MS are derived based on a preamble signal, which is an orthogonal frequency division multiple access (OFDMA) symbol that is transmitted at the beginning of each OFDMA frame.
Similarly, wireless networks that employ third-generation partnership project long-term evolution (3GPP-LTE) compliant architectures employ uplink (UL) reference signals (RSs), which are scheduled to user equipment (subscriber stations (SSs)) within a 3GPP-LTE communication system. Respective sequences of the RSs are used to uniquely identify an SS and, when transmitted from the SS to a serving base station (BS), may be used by the serving BS in channel estimation and channel assignment. The RS sequences may be created through a number of different techniques.
As currently agreed, 3GPP-LTE compliant BSs are configured to signal a number of associated channel sounding control bits (to SSs) on a physical downlink control channel (PDCCH). The SSs decode the channel sounding control bits to determine an appropriate channel sounding RS for transmission. The channel sounding control bits may specify parameters such as a bandwidth (BW), a cyclic shift (CS), and a hopping pattern (HP), among other signal characteristics, to designate a particular channel sounding RS for transmission from a given SS. As currently agreed, 3GPP-LTE compliant systems employ the same number of channel sounding control bits to specify a CS of a channel sounding RS, irrespective of an associated channel sounding bandwidth.